Nitrogen as Horse, Earth, and Air

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Matthew writes:

“My tattoo is taken from a 1950’s biology textbook. The reason it means so much to me is because of the relevence of the nitrogen cycle to the cycle of life. The horse dies, which feeds the plant, which feeds the horse. Its really quite beautiful.”Carl writes: We are each fleeting intersections of the Earth’s biogeochemical cycles, the paths of nitrogen, carbon, oxygen, and the other elements. The carbon cycle is the most familiar of those cycles today, because we are adjusting its knobs so that more carbon is shooting into the atmosphere than was the case before the Industrial Revolution, trapping heat from the sun. If we were to shut the knob off, atmospheric carbon would slowly subside over hundreds of thousands of years as it flowed further on through the carbon cycle, to the bottom of the ocean and ultimately into the bowels of the Earth.

The nitrogen cycle is important as well, and we are also adjusting its knobs. Today the nitrogen entering the world’s soil is moving at twice its natural rate, thanks to our production of fertilizers and burning of fossil fuels. The nitrogen that gets into streams flows out to the oceans where it triggers runaway explosions of microbes, leading to oxygen-free “dead zones” in places like the Baltic Sea and the Gulf of Mexico. These dead zones would be far bigger if not for the help we get from a hidden part of the nitrogren cycle–bacteria in the soil and banks of streams and rivers. Some of these microbes have the biochemical wherewithal to pull nitrogen out of the water and turn it into molecular nitrogen or nitrous oxygen (N20), which diffuses into the air. But these bacteria cannot turn the knobs all the way back; the more nitrogen they are given, the less efficient they get at converting it. As the world’s population grows and releases more nitrogen, the hidden parts of its cycle may come painfully to light.

[Image via Wikipedia]